Shape effect on axially loaded high strength CFST stub columns

In this paper, the results of an experimental investigation of 12 concrete-filled steel tubular (CFST) stub columns subjected to concentric loads are presented. In this program, different cross-sectional shapes are considered: circular, square and rectangular. In order to study the effect of the concrete infill strength in the ultimate capacity of the columns, two types of concrete infill are employed: normal and high strength concrete of grades C30 and C90 respectively. The specimens are classified into three different series so all the columns of a series have equivalent cross-sectional area to perform a proper comparison and draw consistent conclusions. During the tests, the response in terms of load versus column shortening is registered. In view of the experimental results, the dependency of the type of response and failure mode on the cross-sectional shape and type of infill of the columns is analysed. Besides, the influence of the concrete infill, the result of the composite action and the level of ductility are also studied. Finally, the experimental ultimate loads of the specimens are compared with the corresponding failure loads given by the codes. In this case, comparison showed that Eurocode 4 and the Chinese and Australian standards overestimate the failure load of the specimens, particularly for square and rectangular CFST columns. The American code tends to be more conservative in its predictions for circular columns, although it is still unsafe for those with square and rectangular steel tubes.